In some laser printers, electrostatically charged toner particles are transferred from a developer roller that is partially exposed to toner inside of the toner cartridge's toner reservoir, to a photoreceptive drum that is also part of the toner cartridge. In some cartridges, a foam toner adder roller is positioned in the supply hopper to pick up toner and push it against the developer roller to ensure that the developer roller has a sufficient toner supply. In some applications, two blades are mounted on the toner reservoir housing and make contact with the developer roller—a doctor blade, which may be made of steel or another substantially rigid material, meters the thickness of the toner layer that can be transferred from the developer roller to the photoreceptive drum, and a sealing blade, which may be made of polyester film or a similarly flexible material, seals the gap between the developer roller and the toner reservoir housing to prevent toner from leaking out of the toner reservoir through the gap.
After the layer of toner is transferred to the developer roller, it is transferred to those areas of the normally negatively charged photoreceptive drum that have been positively charged by the printer's laser beam to correspond to the desired printed image. The negatively charged toner transfers only to those areas of the photoreceptive drum that have been positively charged by the laser beam, and toner is repelled from those areas of the photoreceptive drum that remain negatively charged. After the toner particles are transferred to the photoreceptive drum, they are transferred to the media that is being printed, such as a piece of paper. This transfer is facilitated by a positively charged transfer roller that is located below the media. The transfer roller has a greater positive charge than the positively charged areas of the photoreceptive drum, and therefore pulls the negatively charged toner away from the photoreceptive drum. Ideally, all of the toner on the drum is transferred to the media, but in reality, relatively small amounts of toner can remain attached to the photoreceptive drum instead of being transferred to the paper. After the photoreceptive drum has transferred toner to the media, it passes over a primary charge roller that “erases” the positively charged areas of the photoreceptive drum such that substantially the entire photoreceptive drum is negatively charged. The photoreceptive drum then returns to the laser beam and is selectively positively charged for a subsequent printing cycle.
To prevent errant toner from remaining on the photoreceptive drum after the toner has been transferred to the media, many toner cartridges also incorporate a flexible wiper or wiper blade that is positioned against the photoreceptive drum at a location “upstream” of where the photoreceptive drum contacts the primary charge roller. The wiper blade wipes errant toner that remains attached to the photoreceptive drum into a toner waste reservoir as it passes by the wiper blade. The toner waste reservoir can also be equipped with a recovery blade that functions similar to the sealing blade and seals the gap between the photoreceptive drum and the toner waste reservoir housing to prevent waste toner from leaking out of the waste reservoir.
Used toner cartridges can be refurbished to allow the cartridge to be reused after the initial toner supply has become low or depleted. When a cartridge is refurbished, components of the cartridge such as the various drums and rollers, the doctor blade, the wiper blades, the various sealing and recovery blades, and the like, may be checked to see if they need to be replaced or, if possible, refurbished.